Production of glandular trichomes responds to water stress and temperature in silver birch (Betula pendula) leaves

Abstract

Silver birch (Betula pendula Roth) allocates substantial resources to the production of glandular trichomes. If these trichomes can protect trees from temperature and water stress, their production would be expected to increase under these conditions. We studied how glandular trichome density and number in the leaves of two-year-old silver birch plantlets respond to single and combined treatments of elevated temperature (+1 degrees C) and three different levels of soil moisture (low, normal, and excess watering). Moreover, we quantified the seasonal variation in trichome density in mature long-shoot leaves of young, greenhouse-grown silver birches. Our results demonstrate clear differences between responses of glandular trichomes on different leaf surfaces. On the adaxial leaf surface, both drought and elevated temperature reduced the production of glandular trichomes. Interestingly, this response was absent in plants subjected to the combined treatment. Glandular trichome production on the abaxial leaf surface increased considerably in leaves produced during the growing season, reflecting a seasonal trend. Maintaining a strong seasonal increase in trichome production of abaxial surfaces even in low-water conditions suggests an important, though still unknown, role for abaxial glandular trichomes. In silver birch stems, those trichomes are strongly responsible for herbivore defense.